Memory deficits at 0.6 MPa ambient air pressure.

We investigated the effects of an elevated ambient air pressure of 0.6 MPa on verbal memory performance. Twenty-four experienced divers were compressed in a dry hyperbaric chamber to pressures equivalent to 0.5 meters of seawater (msw) (n = 12) and 50 msw (n = 12). Verbal memory was assessed by free recall and recognition of visually presented word lists. The testing procedure specified learning and testing at surface, learning at surface and testing at depth, learning and testing at depth, and learning at depth and testing at surface. Non-specific stress was assessed by measurement of salivary cortisol, heart rate, and subjective stress before, during, and after the dives. The 50-msw dive group showed a significant decrease of free recall performance when the material was learned at depth (P < 0.01). However, only postdive recall of material learned at depth remained significantly impaired (P < 0.05), whereas recognition performance was normal. For both groups no significant effects of depth on the investigated stress indices were obtained. These results are taken as evidence that inert gas narcosis may interfere with encoding and/or retrieval of verbal information, although the possibility that other stressors in the hyperbaric environment contributed to these deficits cannot be eliminated entirely.